APM_Control: suppress roll/pitch D term in ground_mode

prevent oscillations which are quite common

libraries/APM_Control/AP_PitchController.cpp

@@ -144,7 +144,7 @@ AP_PitchController::AP_PitchController(AP_AHRS &ahrs, const AP_Vehicle::FixedWin
 /*
   AC_PID based rate controller
 */
-int32_t AP_PitchController::_get_rate_out(float desired_rate, float scaler, bool disable_integrator, float aspeed)
+int32_t AP_PitchController::_get_rate_out(float desired_rate, float scaler, bool disable_integrator, float aspeed, bool ground_mode)
 {
     const float dt = AP::scheduler().get_loop_period_s();
     const float eas2tas = _ahrs.get_EAS2TAS();
@@ -196,6 +196,10 @@ int32_t AP_PitchController::_get_rate_out(float desired_rate, float scaler, bool
 
     // sum components
     float out = pinfo.FF + pinfo.P + pinfo.I + pinfo.D;
+    if (ground_mode) {
+        // when on ground suppress D and half P term to prevent oscillations
+        out -= pinfo.D + 0.5*pinfo.P;
+    }
 
     // remember the last output to trigger the I limit
     _last_out = out;
@@ -226,7 +230,7 @@ int32_t AP_PitchController::get_rate_out(float desired_rate, float scaler)
 	    // If no airspeed available use average of min and max
         aspeed = 0.5f*(float(aparm.airspeed_min) + float(aparm.airspeed_max));
 	}
-    return _get_rate_out(desired_rate, scaler, false, aspeed);
+    return _get_rate_out(desired_rate, scaler, false, aspeed, false);
 }
 
 /*
@@ -278,7 +282,7 @@ float AP_PitchController::_get_coordination_rate_offset(float &aspeed, bool &inv
 // 4) minimum FBW airspeed (metres/sec)
 // 5) maximum FBW airspeed (metres/sec)
 //
-int32_t AP_PitchController::get_servo_out(int32_t angle_err, float scaler, bool disable_integrator)
+int32_t AP_PitchController::get_servo_out(int32_t angle_err, float scaler, bool disable_integrator, bool ground_mode)
 {
 	// Calculate offset to pitch rate demand required to maintain pitch angle whilst banking
 	// Calculate ideal turn rate from bank angle and airspeed assuming a level coordinated turn
@@ -331,7 +335,7 @@ int32_t AP_PitchController::get_servo_out(int32_t angle_err, float scaler, bool
         desired_rate *= (1 - roll_prop);
     }
 
-    return _get_rate_out(desired_rate, scaler, disable_integrator, aspeed);
+    return _get_rate_out(desired_rate, scaler, disable_integrator, aspeed, ground_mode);
 }
 
 void AP_PitchController::reset_I()

libraries/APM_Control/AP_PitchController.h

@@ -16,8 +16,8 @@ public:
     AP_PitchController(const AP_PitchController &other) = delete;
     AP_PitchController &operator=(const AP_PitchController&) = delete;
 
-	int32_t get_rate_out(float desired_rate, float scaler);
-	int32_t get_servo_out(int32_t angle_err, float scaler, bool disable_integrator);
+    int32_t get_rate_out(float desired_rate, float scaler);
+    int32_t get_servo_out(int32_t angle_err, float scaler, bool disable_integrator, bool ground_mode);
 
 	void reset_I();
 
@@ -58,7 +58,7 @@ private:
 
     AP_Logger::PID_Info _pid_info;
 
-    int32_t _get_rate_out(float desired_rate, float scaler, bool disable_integrator, float aspeed);
+    int32_t _get_rate_out(float desired_rate, float scaler, bool disable_integrator, float aspeed, bool ground_mode);
     float   _get_coordination_rate_offset(float &aspeed, bool &inverted) const;
 
     AP_AHRS &_ahrs;

libraries/APM_Control/AP_RollController.cpp

@@ -129,7 +129,7 @@ AP_RollController::AP_RollController(AP_AHRS &ahrs, const AP_Vehicle::FixedWing
 /*
   AC_PID based rate controller
 */
-int32_t AP_RollController::_get_rate_out(float desired_rate, float scaler, bool disable_integrator)
+int32_t AP_RollController::_get_rate_out(float desired_rate, float scaler, bool disable_integrator, bool ground_mode)
 {
     const float dt = AP::scheduler().get_loop_period_s();
     const float eas2tas = _ahrs.get_EAS2TAS();
@@ -185,6 +185,10 @@ int32_t AP_RollController::_get_rate_out(float desired_rate, float scaler, bool
 
     // sum components
     float out = pinfo.FF + pinfo.P + pinfo.I + pinfo.D;
+    if (ground_mode) {
+        // when on ground suppress D term to prevent oscillations
+        out -= pinfo.D + 0.5*pinfo.P;
+    }
 
     // remember the last output to trigger the I limit
     _last_out = out;
@@ -207,7 +211,7 @@ int32_t AP_RollController::_get_rate_out(float desired_rate, float scaler, bool
 */
 int32_t AP_RollController::get_rate_out(float desired_rate, float scaler)
 {
-    return _get_rate_out(desired_rate, scaler, false);
+    return _get_rate_out(desired_rate, scaler, false, false);
 }
 
 /*
@@ -219,7 +223,7 @@ int32_t AP_RollController::get_rate_out(float desired_rate, float scaler)
  3) boolean which is true when stabilise mode is active
  4) minimum FBW airspeed (metres/sec)
 */
-int32_t AP_RollController::get_servo_out(int32_t angle_err, float scaler, bool disable_integrator)
+int32_t AP_RollController::get_servo_out(int32_t angle_err, float scaler, bool disable_integrator, bool ground_mode)
 {
     if (gains.tau < 0.05f) {
         gains.tau.set(0.05f);
@@ -236,7 +240,7 @@ int32_t AP_RollController::get_servo_out(int32_t angle_err, float scaler, bool d
         desired_rate = gains.rmax_pos;
     }
 
-    return _get_rate_out(desired_rate, scaler, disable_integrator);
+    return _get_rate_out(desired_rate, scaler, disable_integrator, ground_mode);
 }
 
 void AP_RollController::reset_I()

libraries/APM_Control/AP_RollController.h

@@ -16,8 +16,8 @@ public:
     AP_RollController(const AP_RollController &other) = delete;
     AP_RollController &operator=(const AP_RollController&) = delete;
 
-	int32_t get_rate_out(float desired_rate, float scaler);
-	int32_t get_servo_out(int32_t angle_err, float scaler, bool disable_integrator);
+    int32_t get_rate_out(float desired_rate, float scaler);
+    int32_t get_servo_out(int32_t angle_err, float scaler, bool disable_integrator, bool ground_mode);
 
 	void reset_I();
 
@@ -63,7 +63,7 @@ private:
 
     AP_Logger::PID_Info _pid_info;
 
-    int32_t _get_rate_out(float desired_rate, float scaler, bool disable_integrator);
+    int32_t _get_rate_out(float desired_rate, float scaler, bool disable_integrator, bool ground_mode);
 
     AP_AHRS &_ahrs;
 };